1. Field of Invention
The invention relates to a method for producing a finished part comprising a zone which forms a door for an airbag and is designed to allow a passageway for the airbag to be created, as well as to such a part and to an assembly comprising the part.
2. Description of the Prior Art
More particularly the invention has applications in the field of automotive interior design, where it is especially relevant to the production of facia panels and door panels.
The object of the invention is to find a straightforward, reliable and inexpensive way of producing durable and reliable parts that enable a passageway to be created in a satisfactory manner.
In order to produce such a part, U.S. Pat. No. 5,395,668 and FR-B-2 725 950 disclose a method featuring the following steps:
a) producing a part comprising a support element made from plastics material(s) which is of reduced thickness compared to its other dimensions, and a connecting sheet which extends substantially along the surface of said support element,
b) incorporating in the part the special zone which forms a door delimited by a periphery constituted by an embrittled portion which has been mechanically weakened between two extremities and by an articulating portion which defines, between said two extremities, an articulation axis overlapped by the sheet.
However, this method is not entirely satisfactory. In particular, as far as the airbag is concerned, opening the door gives rise to fractures and even cracks, which tend to propagate within the part. Since these fractures or cracks are not restricted to the articulating portion, there is a danger of fragments of said part breaking away and being projected at the occupants of the vehicle and injuring them. Furthermore, there is a dispersion of the force deployed by the airbag, requiring the airbag to exert very great pressures to succeed in opening up the door.
Although it would have been possible to employ quality materials that are able to withstand stresses without fracturing, this solution is nevertheless comparatively expensive.
In order to resolve this problem the invention proposes that:
the connecting sheet employed presents a greater length and breadth than those of the special zone, and
during stage b), the embrittled portion is produced in such a manner that the connecting sheet is present to either side of the embrittled portion along at least the major part of said portion, and that the connecting sheet is present over at least the greater part of the special zone.
Accordingly, the retaining sheet is arranged in that section of the part which shows the greatest tendency to fracture on account of the mechanical stresses, and catches any fragments.
The function of the connecting sheet in the present invention is therefore different from those in U.S. Pat. No. 5,395,668 and FR-B-2 725 950, where it acts as a reinforced articulation means. That is also why in those documents it is disposed near to the articulating portion.
Accordingly, if appropriate it would be possible to provide for a connecting sheet to be present over the major part of the door in order to catch the fragments, and to have a connecting sheet present in the vicinity of the articulating portion in order to reinforce the joint if the mechanical stresses involved called for this.
The length and breadth of the sheet represent its external dimensions perpendicularly and along the articulation axis, respectively.
According to one preferred application of the invention, during stage b), in at least part of the embrittled portion a cutout is simultaneously made in the sheet and the support is mechanically weakened by excising a part of its thickness.
This straightforward solution makes it possible on the one hand to quickly obtain a particularly efficient reinforcement of the support as far as the edge of the embrittled portion, and on the other hand to satisfactorily weaken said support mechanically, by precise positioning, relative to one another, of the cutout in the sheet and the mechanical weakening of the support. The cutout is preferably continuous and runs through the full thickness of the sheet, although this is not necessary.
In order to resolve the foregoing problems still more effectively and simply, the invention proposes:
during stage a), carrying out the following operations:
introducing the connecting sheet into a mould cavity, and
introducing the plastics material into the mould cavity, said plastics material making contact with the sheet,
during stage b), producing the embrittled portion in such a manner that it is wholly and strictly enclosed within the sheet.
Accordingly, the connecting sheet surrounds the perimeter (the entire periphery) of the door and covers the whole of the door. On either side of the embrittled portion the support is reinforced by the sheet over the whole of said portion. The moulding process makes it possible to produce the part in a straightforward and satisfactory manner, especially by making it possible to place the sheet in position easily, with the result that said sheet is present everywhere that it is desired to produce the cutout.
In order to obtain even better quality parts in a straightforward and reliable manner, the invention proposes:
the use of a mould comprising a mould cavity, a female die, a male die and an insert adapted to be moved between a retracted position and an advanced position, said movable insert being inserted into a cavity in the male die, thereby producing a slot between it and the male die when the insert is in the retracted position and moving further away from the male die when it is displaced towards the advanced position,
during stage a), introducing the sheet into the mould cavity, with the movable insert advanced; then by retracting the movable insert a folded portion of the sheet is set in said slot; the plastics material is now introduced into the mould cavity.
In this manner a part is obtained wherein the sheet is in the form of a loop facing the articulating portion. The pivoting of the door about the articulation axis is thus facilitated by the excess length of the sheet formed by this loop. Moreover, the production of the support, its connection to the sheet and the accomplishment of this loop are all brought about in a single operation.
According to a further practical feature, the invention proposes:
during stage a), producing the part in such a way that the sheet is present over all or at least the majority of the part, perpendicularly to the articulation axis,
attaching the part by fixing it to a body, and
joining the sheet to the body.
The presence of the sheet over all or at least the majority of the part perpendicularly to the articulation axis considerably reduces the risk of fragments of the part being thrown off. The joint between the sheet and the body ensures that the part will continue to be retained in relation to the body, in so far as there is no danger that the inflexible sheet will fracture.
In order to facilitate the fixing, i.e. connection, of the sheet to the body, the invention proposes:
during stage a), sticking out a tongue of said sheet from the mould cavity,
and joining said tongue of the sheet to the body.
A further object of the invention is a composite finished part. U.S. Pat. No. 5,395,668 and FR-B-2 725 950 describe a part comprising:
a support element made of plastic and having a reduced thickness compared to its other dimensions,
a connecting sheet joined to the support element, said part featuring a special zone which forms a door for an airbag and is designed to allow the creation of a passageway, said zone being delimited by a periphery constituted by an embrittled portion having two extremities and an articulating portion which, between said two extremities, defines an articulation axis overlapped by the sheet.
However, this part presents the drawbacks outlined above. In order to overcome these drawbacks the invention proposes:
that along at least the major part of the embrittled portion the sheet should be present on either side of said portion, and
that the sheet should cover the majority of the special zone.
According to another advantageous feature, the invention proposes that the sheet should extend, perpendicularly to the articulation axis, beyond the articulating portion and at least as far as the edge of the part.
This reduces the risk that the pressure exerted by the airbag on the door and the resulting inertia on said door will cause the fracture or at least the start of a fracture of the part in a direction perpendicular to the articulation axis.
The invention furthermore relates to an assembly incorporating the part. According to the invention this assembly is characterised by the fact that:
it additionally comprises a body onto which the part is fixed, and
the sheet is joined to the body.